Backlight generation with local dimming for liquid crystal panel having arbitrary shape

Abstract

In a liquid crystal display (LCD), a liquid crystal (LC) panel has a display area of arbitrary shape. A light-emitting area of a backlight panel is partitioned into zones for providing local dimming to the LC panel. The LC panel is partitioned into display regions. An apparatus for controlling the LC panel and the backlight panel has zone registers each recording a proportion of area of a zone covered by a corresponding display region. The apparatus computes a dimming factor for the zone according to its recorded proportion and pixel data of a portion of image located on the zone, allowing local dimming to be provided without requiring boundary information of the display area. A two-phase arrangement is used to calculate the dimming factor, achieving local dimming to save power in backlight generation while reducing a potential loss of image brightness in high-brightness part of the image portion.

What is claimed is: 
     
       1. An apparatus for controlling a liquid crystal (LC) panel and a backlight panel to display a rectangular raw image, the backlight panel being used for illuminating the LC panel, the LC panel having a display area arbitrary in shape, a light-emitting area of the backlight panel being partitioned into a plurality of zones individually controllable for providing local dimming to the LC panel, the plurality of zones defining a grid used for partitioning the display area into a plurality of display regions such that an individual display region is illuminated by a corresponding zone of the backlight panel, the apparatus comprising:
 a plurality of zone registers for the plurality of zones, a respective zone register for the corresponding zone being used to record a proportion of area of the corresponding zone covered by the individual display region; and 
 one or more computing units communicable with the plurality of zone registers, the one or more computing units being configured to control the corresponding zone to generate backlight with a dimming factor determined according to plural pixel data of a portion of the image located on the corresponding zone and according to the proportion of area of the corresponding zone covered by the individual display region, allowing local dimming to be provided without a need for boundary information of the display area. 
 
     
     
       2. The apparatus of  claim 1 , wherein the one or more computing units are further configured to execute a process comprising the steps of:
 determining a number of pixels on the individual display region according to the proportion of area of the corresponding zone covered by the individual display region; 
 receiving a plurality of pixel data of the image portion; 
 computing a plurality of pixel brightness levels of the image portion according to the plurality of pixel data; 
 determining the dimming factor according to the plurality of pixel brightness levels and the number of pixels on the individual display region; 
 controlling the corresponding zone to generate backlight with the dimming factor; 
 computing a plurality of modified pixel data of the image portion from the plurality of pixel data according to at least the dimming factor; and 
 sending the plurality of modified pixel data to the LC panel for displaying the image portion on the individual display region. 
 
     
     
       3. The apparatus of  claim 2 , wherein the determination of the dimming factor comprises the steps of:
 computing a first average value,  B , by  B =N −1  Σ i=1, . . . , N  B i , where N is the number of pixels on the individual display region, and {B i |i=1, . . . , N} is the plurality of pixel brightness levels; 
 computing a second average value,  B′ , by  B′ =N −1  Σ i=1, . . . , N  ƒ(B i ), where ƒ(x) is a function satisfying that ƒ(x)=x for x≤ B  and ƒ(x)>x for x> B , thereby causing a first pixel brightness level greater than the first average value to receive a greater weight in computing the second average value than a second pixel brightness level that is less than the first average value where the first and second pixel brightness levels are in the plurality of pixel brightness levels, and hence causing the second average value to be inflated from the first average value; and 
 determining the dimming factor to be a lower one of a candidate dimming factor and 100%, the candidate dimming factor being a ratio of the second average value to a predetermined maximum brightness level deliverable by the backlight panel, thereby achieving local dimming to save power in backlight generation while reducing a potential loss of image brightness in high-brightness part of the image portion. 
 
     
     
       4. The apparatus of  claim 3 , wherein ƒ(x) is an increasing function and is increasingly divergent as x increases from  B , thereby providing an increasingly greater weight to a third pixel brightness level in computing the second average value as the third pixel brightness level increases from the first average value where the third pixel brightness level is in the plurality of pixel brightness levels. 
     
     
       5. The apparatus of  claim 2 , wherein before controlling the corresponding zone to generate backlight, updating the dimming factor by an updating process comprising the steps of:
 obtaining respective dimming factors determined for neighboring zones immediately adjacent to the corresponding zone, said respective dimming factors forming a plurality of neighboring-zone dimming factors; and 
 if the dimming factor is not less than a threshold value equal to a predetermined percentage of a maximum value in the plurality of neighboring-zone dimming factors, then keeping the dimming factor unchanged, else updating the dimming factor to be the threshold value so as to reduce luminance non-uniformity occurred over the corresponding zone and caused by light leakage to and from the neighboring zones. 
 
     
     
       6. The apparatus of  claim 5 , wherein the predetermined percentage is in a range of 60% to 70%. 
     
     
       7. The apparatus of  claim 2 , wherein before controlling the corresponding zone to generate backlight, updating the dimming factor by an updating process comprising the steps of:
 obtaining respective dimming factors determined for neighboring zones immediately adjacent to the corresponding zone, the dimming factor and said respective dimming factors collectively forming a plurality of dimming factors obtained by a cluster consisting of the corresponding zone and the neighboring zones; and 
 filtering the plurality of dimming factors obtained by the cluster with a nonlinear spatial filter to update the dimming factor, wherein the nonlinear spatial filter is configured to reduce luminance non-uniformity occurred over the corresponding zone and caused by light leakage to and from the neighboring zones. 
 
     
     
       8. The apparatus of  claim 2 , wherein the plurality of modified pixel data is computed from the plurality of pixel data according to the determined dimming factor and a gamma value of the LC panel. 
     
     
       9. The apparatus of  claim 2 , wherein:
 in the plurality of pixel data, an individual pixel data associated with a corresponding pixel of the image portion consists of a plurality of subpixel data, each subpixel data indicating a pixel brightness level of a color component in forming the image portion at the corresponding pixel; and 
 in computing the plurality of pixel brightness levels of the image portion, a pixel brightness level of the image portion displayed at the corresponding pixel is computed as a maximum value in the plurality of subpixel data. 
 
     
     
       10. A liquid crystal display (LCD) comprising:
 a liquid crystal (LC) panel and a backlight panel, the backlight panel being used for illuminating the LC panel, the LC panel having a display area arbitrary in shape, a light-emitting area of the backlight panel being partitioned into a plurality of zones individually controllable for providing local dimming to the LC panel, the plurality of zones defining a grid used for partitioning the display area into a plurality of display regions such that an individual display region is illuminated by a corresponding zone of the backlight panel; and 
 the apparatus for controlling the LC panel and the backlight panel to display a rectangular raw image as set forth in  claim 1 . 
 
     
     
       11. The LCD of  claim 10 , wherein the corresponding zone is formed with a plurality of mini light emitting diodes (mLEDs) distributed over the corresponding zone, the plurality of mLEDs being controllable by the apparatus to collectively generate backlight with the dimming factor. 
     
     
       12. A method for controlling a liquid crystal (LC) panel and a backlight panel to display a rectangular raw image, the backlight panel being used for illuminating the LC panel, the LC panel having a display area arbitrary in shape, a light-emitting area of the backlight panel being partitioned into a plurality of zones individually controllable for providing local dimming to the LC panel, the plurality of zones defining a grid used for partitioning the display area into a plurality of display regions such that an individual display region is illuminated by a corresponding zone of the backlight panel, the method comprising the steps of:
 determining a number of pixels on the individual display region; 
 receiving a plurality of pixel data of a portion of the image located on the corresponding zone; 
 computing a plurality of pixel brightness levels of the image portion according to the plurality of pixel data; 
 determining a dimming factor used in generating backlight for the corresponding zone according to the plurality of pixel brightness levels and the number of pixels on the individual display region in an absence of boundary information of the display area, thereby allowing local dimming to be provided without a need for such boundary information; 
 controlling the corresponding zone to generate backlight with the dimming factor; 
 computing a plurality of modified pixel data of the image portion from the plurality of pixel data according to at least the dimming factor; and 
 sending the plurality of modified pixel data to the LC panel for displaying the image portion on the individual display region. 
 
     
     
       13. The method of  claim 12 , wherein the determination of the dimming factor comprises the steps of:
 computing a first average value,  B , by  B =N −1  Σ i=1, . . . , N  B i , where N is the number of pixels on the individual display region, and {B i |i=1, . . . , N} is the plurality of pixel brightness levels; 
 computing a second average value,  B′ , by  B′ =N −1  Σ i=1, . . . , N  ƒ(B i ), where ƒ(x) is a function satisfying that ƒ(x)=x for x≤ B  and ƒ(x)>x for x> B , thereby causing a first pixel brightness level greater than the first average value to receive a greater weight in computing the second average value than a second pixel brightness level that is less than the first average value where the first and second pixel brightness levels are in the plurality of pixel brightness levels, and hence causing the second average value to be inflated from the first average value; and 
 determining the dimming factor to be a lower one of a candidate dimming factor and 100%, the candidate dimming factor being a ratio of the second average value to a predetermined maximum brightness level deliverable by the backlight panel, thereby achieving local dimming to save power in backlight generation while reducing a potential loss of image brightness in high-brightness part of the image portion. 
 
     
     
       14. The method of  claim 13 , wherein ƒ(x) is an increasing function and is increasingly divergent as x increases from  B , thereby providing an increasingly greater weight to a third pixel brightness level in computing the second average value as the third pixel brightness level increases from the first average value where the third pixel brightness level is in the plurality of pixel brightness levels. 
     
     
       15. The method of  claim 12 , wherein before controlling the corresponding zone to generate backlight, updating the dimming factor by an updating process comprising the steps of:
 obtaining respective dimming factors determined for neighboring zones immediately adjacent to the corresponding zone, said respective dimming factors forming a plurality of neighboring-zone dimming factors; and 
 if the dimming factor is not less than a threshold value equal to a predetermined percentage of a maximum value in the plurality of neighboring-zone dimming factors, then keeping the dimming factor unchanged, else updating the dimming factor to be the threshold value so as to reduce luminance non-uniformity occurred over the corresponding zone and caused by light leakage to and from the neighboring zones. 
 
     
     
       16. The method of  claim 15 , wherein the predetermined percentage is in a range of 60% to 70%. 
     
     
       17. The method of  claim 12 , wherein before controlling the corresponding zone to generate backlight, updating the dimming factor by an updating process comprising the steps of:
 obtaining respective dimming factors determined for neighboring zones immediately adjacent to the corresponding zone, the dimming factor and said respective dimming factors collectively forming a plurality of dimming factors obtained by a cluster consisting of the corresponding zone and the neighboring zones; and 
 filtering the plurality of dimming factors obtained by the cluster with a nonlinear spatial filter to update the dimming factor, wherein the nonlinear spatial filter is configured to reduce luminance non-uniformity occurred over the corresponding zone and caused by light leakage to and from the neighboring zones. 
 
     
     
       18. The method of  claim 12 , wherein the plurality of modified pixel data is computed from the plurality of pixel data according to the determined dimming factor and a gamma value of the LC panel. 
     
     
       19. The method of  claim 12 , wherein:
 in the plurality of pixel data, an individual pixel data associated with a corresponding pixel of the image portion consists of a plurality of subpixel data, each subpixel data indicating a pixel brightness level of a color component in forming the image portion at the corresponding pixel; and 
 in computing the plurality of pixel brightness levels of the image portion, a pixel brightness level of the image portion displayed at the corresponding pixel is computed as a maximum value in the plurality of subpixel data.